I would go with the morning sun site, myself. Those occasional hot, sunny days can do damage, unless the sun doesn't start until fairly late in the afternoon, and then it may not get enough light intensity for full color--coming out more chartreuse than orange.

I have to disagree. They really need dappled sun but if the morning dew sits on the leaves the sun will scorch them. I think that the afternoon sun won't be so intense.

Afternoon sun is the sun that burns people though. . have a really good look at your garden and see if there isn't a place somewhere that mimics open light woodland. an if one site is windier than the other that's a consideration too as strong winds scorch the leaves even more than strong sun.

The critical time is between 11 and 3, and only in summer, as far as sun exposure is concerned for a japanese acer, but wind is even worse, as Steragram says.

And that story about dewdrops acting as magnifying glasses and burning leaves is a gardening myth. The focal length of the drops is too long to concentrate the sun enough.

Thanks everyone.

Tug: yep agree re water droplets, that myth persists following original experiments with glass droplets and not water. Jimmythe one, here's the real deal on that subject, just for interest's sake

http://www.abc.net.au/science/articles/2016/06/07/4475079.htm

That myth never fit my observations, and the sun here is as strong as anywhere in the world. I saw that article too, but I couldn't find it in time to include it--glad you remembered it! :)